1. Field of the Invention
The present invention relates to a semiconductor device, more specifically, to the wiring or electrode structure of a compound semiconductor device.
2. Background Art
As a material for a compound semiconductor device, a compound semiconductor, such as GaAs and InP, is used. As an electrode and wiring of a compound semiconductor device, gold (Au) is widely used.
These electrode and wiring are subjected to heat during the manufacturing process, or when used as a product. At this time, Au contained in the electrode or wiring causes interdiffusion between the electrode or wiring and the compound semiconductor or the aluminum (Al) electrode. Then the characteristics of the semiconductor device are changed or deteriorated.
In Japanese Unexamined Patent Publication No. 2004-22773, an electrode structure wherein a molybdenum (Mo) metallic layer and a gold (Au) metallic layer are sequentially stacked on a nickel (Ni) metallic layer is disclosed. Since the melting point of a Mo metallic layer is high, interdiffusion between the Ni metallic layer and the Au metallic layer can be prevented.
However, Mo is relatively inferior in moisture resistance and corrosion resistance. Therefore, when a compound semiconductor device using Mo as the diffusion preventing layer is exposed to water, an aqueous solution, or a high-temperature or high-humidity environment, it is easily corroded. Thereby, defects, such as the elevation of device resistance, poor conduction, and short-circuiting between wirings, will occur.